Prospects for the stimulation, control, and study of high-gain linac-driven x-ray free-electron laser (FEL) interactions using high-power IR/visible/UV lasers

In recent years, substantial design studies have been initiated on angstrom-wavelength free-electron laser (FEL) schemes based on driving highly compressed electron bunches from a multi-GeV linac through long (30 m - 100 m) undulators. Within the context of the technologies considered, the attainment of such parameters involves the development of large, complex, and highly costly technical systems, and the preliminary or concomitant execution of complex demonstration experiments to study self-amplified spontaneous emission (SASE), or other gain mechanisms, on lower-energy linacs at longer wavelengths. In all phases of the FEL gain processes undertaken by such studies, the strength of the FEL radiation field in the electron bunch rest frame is typically no more than a fraction of a percent of the transformed undulator field. In contrast, recently developed terawatt lasers in the IR/visible/UV regimes could be made to match or exceed a transformed undulator's field strength in an electron bunch of suitable energy, enabling high-level control of the FEL gain process, and thereby of the spectral and temporal parameters of the FEL output. Due to the highly non-linear nature of the radiation/electron bunch interaction, control and generation of high-power FEL radiation with such lasers could, in principle, be extended well into the soft x-ray regime. In this presentation we discuss selected schemes for attaining high-power x ray FEL output in radiation pulses of conventional or ultra-short duration, and examine ways in which lower-cost, equivalent studies of SASE gain at lower energies could be achieved. Selected applications to particle beam diagnostics are also examined.